Effects of suboccipital release with craniocervical flexion exercise on craniocervical alignment and extrinsic cervical muscle activity in subjects with forward head posture

BackgroundForward head posture is a head-on-trunk malalignment, which results in musculoskeletal dysfunction and neck pain. To improve forward head posture, both the craniocervical flexion exercise and the suboccipital release technique have been used. Objectives: The purpose of this study was to compare the immediate effects of craniocervical flexion exercise and suboccipital release combined with craniocervical flexion exercise on craniovertebral angle, cervical flexion and extension range of motion, and the muscle activities of the sternocleidomastoid, anterior scalene, and splenius capitis during craniocervical flexion exercise in subjects with forward head posture.MethodsIn total, 19 subjects (7 males, 12 females) with forward head posture were recruited using G-power software. Each subject performed craniocervical flexion exercise and suboccipital release combined with craniocervical flexion exercise in random order. After one intervention was performed, the subject took a 20 min wash out period to minimize any carry-over effect between interventions. Craniovertebral angle, cervical flexion and extension range of motion, and the muscle activities of the sternocleidomastoid, anterior scalene, and splenius capitis were measured. A one-way, repeated-measures ANOVA was used to assess differences between the effects of the craniocervical flexion exercise and suboccipital release combined with craniocervical flexion exercise interventions in the same group.ResultsCraniovertebral angle (p < 0.05), cervical flexion range of motion (p < 0.05), and cervical extension range of motion (p < 0.001) were significantly greater after suboccipital release combined with craniocervical flexion exercise compared to craniocervical flexion exercise alone. The muscle activities of the sternocleidomastoid, anterior scalene, and splenius capitis were significantly lower during suboccipital release combined with craniocervical flexion exercise than during craniocervical flexion exercise alone across all craniocervical flexion exercise phases except the first (all p < 0.05).ConclusionThe addition of suboccipital release to craniocervical flexion exercise provided superior benefits relative to craniocervical flexion exercise alone as an intervention for subjects with forward head posture.     

Pain-induced changes in cervical muscle activation do not affect muscle fatigability during sustained isometric contraction

This study investigated whether pain-induced changes in cervical muscle activation affect myoelectric manifestations of cervical muscle fatigue. Surface EMG signals were detected from the sternocleidomastoid and splenius capitis muscles bilaterally from 14 healthy subjects during 20-s cervical flexion contractions at 25% of the maximal force. Measurements were performed before and after the injection of 0.5 ml of hypertonic (painful) or isotonic (control) saline into either the sternocleidomastoid or splenius capitis in two experimental sessions. EMG average rectified value and mean power spectral frequency were estimated throughout the sustained contraction. Sternocleidomastoid or splenius capitis muscle pain resulted in lower sternocleidomastoid EMG average rectified value on the side of pain (P < 0.01). However, changes over time of sternocleidomastoid EMG average rectified value and mean frequency (myoelectric manifestations of fatigue) during sustained flexion were not changed during muscle pain. These results demonstrate that pain-induced modifications of cervical muscle activity do not change myoelectric manifestations of fatigue. This finding has implications for interpreting the mechanisms underlying greater cervical muscle fatigue in people with neck pain disorders.     

Flexion–relaxation ratio in computer workers with and without chronic neck pain

This study evaluated the flexion–relaxation phenomenon (FRP) and flexion–relaxation ratios (FR-ratios) using surface electromyography (sEMG) of the cervical extensor muscles of computer workers with and without chronic neck pain, as well as of healthy subjects who were not computer users. This study comprised 60 subjects 20–45 years of age, of which 20 were computer workers with chronic neck pain (CPG), 20 were computer workers without neck pain (NPG), and 20 were control individuals who do not use computers for work and use them less than 4 h/day for other purposes (CG). FRP and FR-ratios were analyzed using sEMG of the cervical extensors. Analysis of FR-ratios showed smaller values in the semispinalis capitis muscles of the two groups of workers compared to the control group. The reference FR-ratio (flexion relaxation ratio [FRR], defined as the maximum activity in 1 s of the re-extension/full flexion sEMG activity) was significantly higher in the computer workers with neck pain compared to the CG (CPG: 3.10, 95% confidence interval [CI95%] 2.50–3.70; NPG: 2.33, CI95% 1.93–2.74; CG: 1.99, CI95% 1.81–2.17; p < 0.001). The FR-ratios and FRR of sEMG in this study suggested that computer use could increase recruitment of the semispinalis capitis during neck extension (concentric and eccentric phases), which could explain our results. These results also suggest that the FR-ratios of the semispinalis may be a potential functional predictive neuromuscular marker of asymptomatic neck musculoskeletal disorders since even asymptomatic computer workers showed altered values. On the other hand, the FRR values of the semispinalis capitis demonstrated a good discriminative ability to detect neck pain, and such results suggested that each FR-ratio could have a different application.     

Neck and shoulder muscle activity of orthodontists in natural environments

Work related musculoskeletal disorders (WMSDs) are common among dentists and possibly caused by prolonged static load. The aim of this study was to assess the contraction pattern of neck and shoulder muscles of orthodontists in natural environments.Electromyographic (EMG) activity of right sternocleidomastoid and trapezius muscles were recorded by means of portable recorders in eight orthodontists during working conditions, and both active and resting non-working conditions. Recordings were analysed in terms of contraction episode (CE) count, amplitude, and duration.The sternocleidomastoid and trapezius muscles contracted about 40–70 times per hour in the natural environment. Their EMG activity pattern mainly consisted of short-lasting, low-amplitude CEs. The counts and amplitude of sternocleidomastoid CEs did not differ across vocational and non-vocational conditions. The number and amplitude of trapezius CEs were slightly but significantly higher during the vocational condition. There were highly significant (p < 0.001) differences in duration of CEs across conditions, with two to threefold increase in the average duration of trapezius muscle contractions found in the vocational setting.During orthodontic work, operators commonly hold muscular contractions for significantly longer periods than are encountered in non-vocational settings. This behaviour may be associated causally with the increases seen in WMSDs through proposed pathophysiological mechanisms occurring at the motor unit level. Our findings may also be valid for other occupations characterised by seated static postures with precision hand and wrist movements.     

Differential patterns of muscle modification in women with episodic and chronic tension-type headache revealed using surface electromyographic analysis

Tension-type headache (TTH) is a prototypical disorder in which muscular factors play a key role in the pathogenesis. This study was designed to understand muscular dysfunction in patients with episodic (ETTH) and chronic TTH (CTTH) using surface electromyography analysis (SEMG). Women with frequent ETTH (n = 14), CTTH (n = 14) and age-matched controls (n = 13) were recruited. SEMG data were recorded from the masseter, sternocleidomastoid, and upper trapezius muscles during maximum voluntary contraction and sustained voluntary isometric clenching, the neck flexion endurance test and shoulder elevation for 30 s. The root mean square (RMS) and median frequency (MDF) of the SEMG signal were measured throughout the test. The fatigue index, which is the MDF slope during sustained muscle contraction, decreased significantly faster in the ETTH and CTTH groups compared with that in the control (p < 0.05). The mean absolute RMS and relative percentage values at the initial and final period during sustained isometric contraction decreased significantly in the CTTH group (p < 0.05). Furthermore, headache clinical parameters (frequency and duration) were negatively correlated with the amplitude values (p < 0.05). A different muscle firing pattern or some muscle modifications in patients with CTTH may reflect reorganization of the motor-control strategy.     

Age-related differences to neck muscle activation latency as a potential risk factor to fall-related traumatic brain injuries

This investigation examined age-related differences in neck muscle activation latency in response to anterior and posterior postural perturbations to understand the potential implications in fall-related traumatic brain injuries. 57 adults were recruited and categorized into 3 groups based on age: Young (18–30 years old), Young-Old (60–74 years) and Old-Old (75–89 years) group. Study participants underwent six anterior and posterior postural perturbations while bilateral sternocleidomastoid, upper trapezius, and splenius capitis electromyography was collected. Muscle activation latency time was calculated with established procedures. During anterior translations, a significant group effect for muscle activation latency of the right SCM (F(2,43) = 8.786, p < 0.001), right (F(2,34) = 4.838, p = 0.014) and left (F(2,34) = 5.015, p = 0.012) upper trapezius, and right (F(2,45) = 3.195, p = 0.050) and left (F(2,45) = 3.819, p = 0.029) splenius capitis was observed. During posterior translations, a significant group effect for muscle activation latency was observed in the right (F(2,34) = 6.419, p = 0.004) and left (F(2,41) = 5.275, p = 0.009) SCM, and the right (F(2,34) = 4.925, p = 0.013) and left (F(2,32) = 4.055, p = 0.027) upper trapezius. Both older groups displayed longer muscle activation latencies than the young group. The age-related differences in neck muscle activation latency may be placing older adults at a greater risk of fall-related traumatic brain injuries.     

The use of EMG biofeedback for learning of selective activation of intra-muscular parts within the serratus anterior muscle: A novel approach for rehabilitation of scapular muscle imbalance

Motor control and learning possibilities of scapular muscles are of clinical interest for restoring scapular muscle balance in patients with neck and shoulder disorders. The aim of the study was to investigate whether selective voluntary activation of intra-muscular parts within the serratus anterior can be learned with electromyographical (EMG) biofeedback, and whether the lower serratus anterior and the lower trapezius muscle comprise the lower scapula rotation force couple by synergistic activation. Nine healthy males practiced selective activation of intra-muscular parts within the serratus anterior with visual EMG biofeedback, while the activity of four parts of the serratus anterior and four parts of the trapezius muscle was recorded. One subject was able to selectively activate both the upper and the lower serratus anterior respectively. Moreover, three subjects managed to selectively activate the lower serratus anterior, and two subjects learned to selectively activate the upper serratus anterior. During selective activation of the lower serratus anterior, the activity of this muscle part was 14.4 ± 10.3 times higher than the upper serratus anterior activity (P < 0.05). The corresponding ratio for selective upper serratus vs. lower serratus anterior activity was 6.4 ± 1.7 (P < 0.05). Moreover, selective activation of the lower parts of the serratus anterior evoked 7.7 ± 8.5 times higher synergistic activity of the lower trapezius compared with the upper trapezius (P < 0.05). The learning of complete selective activation of both the lower and the upper serratus anterior of one subject, and selective activation of either the upper or lower serratus anterior by five subjects designates the promising clinical application of EMG biofeedback for restoring scapular muscle balance. The synergistic activation between the lower serratus anterior and the lower trapezius muscle was observed in only a few subjects, and future studies including more subjects are required before conclusions of a lower scapula rotation couple can be drawn.     

Optimal whole-body vibration settings for muscle strength and power enhancement in human knee extensors

This study compared the effects of 6-week whole-body vibration (WBV) training programs with different frequency and peak-to-peak displacement settings on knee extensor muscle strength and power. The underlying mechanisms of the expected gains were also investigated. Thirty-two physically active male subjects were randomly assigned to a high-frequency/high peak-to-peak displacement group (HH; n = 12), a low-frequency/low peak-to-peak displacement group (LL; n = 10) or a sham training group (SHAM; n = 10). Maximal voluntary isometric, concentric and eccentric torque of the knee extensors, maximal voluntary isometric torque of the knee flexors, jump performance, voluntary muscle activation, and contractile properties of the knee extensors were assessed before and after the training period. Significant improvement in knee extensor eccentric voluntary torque (P < 0.01), knee flexor isometric voluntary torque (P < 0.05), and jump performance (P < 0.05) was observed only for HH group. Regardless of the group, knee extensor muscle contractile properties (P < 0.05) were enhanced. No modification was observed for voluntary muscle activation or electrical activity of agonist and antagonist muscles. We concluded that high-frequency/high peak-to-peak displacement was the most effective vibration setting to enhance knee extensor muscle strength and jump performance during a 6-week WBV training program and that these improvements were not mediated by central neural adaptations.     

Spectral profile of superficial cervical muscles.

The objective of the study was to determine the median frequency (MF) and mean power frequency (MPF) of the stermodeidomastorial, splenius capitis and trapezius in progressively and linearly increasing isometric cervical flexion and extension. There is a dearth of data on spectral parameters of cervical muscles. Such data have been generated from 40 young adult subjects (21 male and 19 female). The subjects were seated upright in an individually adjusted chair and stabilized with a 4-point Velcro restraint system to stabilize the torso. These subjects exerted isometric flexor and extensor forces in a random sequence on an instrumented resistance device (specifically designed for the study) in a gradual and linearly increasing manner with a visual feedback to their maximal voluntary contraction (MVC) within a 5 s period. Surface EMG was sampled from the sternocleidomastoid, the splenius capitis and the trapezius muscles bilaterally at 1 kHz. The EMG signals were subjected to Fast Fourier Transform (FFT) analysis. Spectral profiles of all muscles in the dimensions of frequency, power, and grade of contraction were plotted. The mean median frequency (MF), mean power frequency (MPF), peak power and total power were analyzed. In the sternocleidomastoid, and the splenius the MF increased with the grade of contraction, widening its bandwidth at higher grades. The trapezius maintained a narrow bandwidth and its MF declined with the grade of contraction.     

Influence of test position on neck muscle fatigue in healthy controls

BackgroundIt has been suggested that increased fatigue of neck muscles could be related to neck pain. However, studies on the matter present contradicting results which could be explained by the different test positions used.PurposeThe purpose of this study was to investigate the influence of test position on muscle fatigue of neck flexor and extensor muscles in healthy controls.MethodsTwenty-five women without neck pain sustained neck flexion and neck extension isometric contractions at 25% and 75% of their maximal voluntary contraction (MVC) in two test positions: sitting and supine lying. Using surface electromyography, the change over time of the median frequency of the power spectrum (MDF slope) of the myoelectric signal of the sternocleidomastoid and splenius capitis muscles was measured and compared between both positions.ResultsAt 75% MVC, splenius capitis muscles presented higher fatigue in lying compared to sitting, while sternocleidomastoid demonstrated no difference between positions. No statistically significant effect of test position was found at 25% MVC for both sternocleidomastoid and splenius capitis muscles as they generally did not present myoelectric manifestations of fatigue.ConclusionThese results underline the need to standardise the test position when investigating neck muscle fatigue, especially for neck extensors at high loads.     

Reduced scapular muscle control and impaired shoulder joint position sense in subjects with chronic shoulder stiffness

The purpose of the present study was to determine (1) if joint position sense (JPS) in subjects with shoulder stiffness (SS) differs from that in controls; (2) if, when JPS is reduced in SS, it is related to scapular muscular activities in the mid/end ranges of motion; and (3) if a person’s function is associated with his or her level of JPS. Eighteen subjects with unilateral SS and 18 controls were included. Each subject performed abduction by self-selecting an end/mid range position. The electromagnetic motion-capturing system collected kinematic data while surface electromyography collected muscle activities (upper trapezius, lower trapezius, and serratus anterior muscles). Subjects were asked to move the upper limb to the target position (end/mid range) accurately without visual guidance. Reduced JPS was observed in subjects with SS (2.7 degrees in mid range, p < 0.05). The JPS was enhanced by an increased scapula muscular activation level in the end range of motion (R = ?0.61 for SS and ?0.41 for controls) and by coordination among muscles’ activation in the mid-range of motion (R = ?0.87 for SS and R = ?0.53 for controls). Impaired JPS was also related to self-reported functional status (R = ?0.56) in subjects with SS. Shoulder JPS in subjects with chronic SS is impaired in comparison with controls. In the mid-range motion, the coordination of scapula muscular activation is related to shoulder JPS. Impaired JPS is also function-related in subjects with SS. These findings suggest that the coordination among scapula muscles’ activation were important to consider in the rehabilitation of patients with chronic SS.     

Electromyography responses of pediatric and young adult volunteers in low-speed frontal impacts

No electromyography (EMG) responses data exist of children exposed to dynamic impacts similar to automotive crashes, thereby, limiting active musculature representation in computational occupant biomechanics models. This study measured the surface EMG responses of three neck, one torso and one lower extremity muscles during low-speed frontal impact sled tests (average maximum acceleration: 3.8 g; rise time: 58.2 ms) performed on seated, restrained pediatric (n = 11, 8–14 years) and young adult (n = 9, 18–30 years) male subjects. The timing and magnitude of the EMG responses were compared between the two age groups. Two normalization techniques were separately implemented and evaluated: maximum voluntary EMG (MVE) and neck cross-sectional area (CSA). The MVE-normalized EMG data indicated a positive correlation with age in the rectus femoris for EMG latency; there was no correlation with age for peak EMG amplitudes for the evaluated muscles. The cervical paraspinous exhibited shorter latencies compared with the other muscles (2–143 ms). Overall, the erector spinae and rectus femoris peak amplitudes were relatively small. Neck CSA-normalized peak EMG amplitudes negatively correlated with age for the cervical paraspinous and sternocleidomastoid. These data can be useful to incorporate active musculature in computational models, though it may not need to be age-specific in low-speed loading environments.     

Strength training,but not endurance training,reduces motor unit discharge rate variability

This study evaluates and compares the effects of strength and endurance training on motor unit discharge rate variability and force steadiness of knee extensor muscles. Thirty sedentary healthy men (age, 26.0 ± 3.8 yrs) were randomly assigned to strength training, endurance training or a control group. Conventional endurance and strength training was performed 3 days per week, over a period of 6 weeks. Maximum voluntary contraction (MVC), time to task failure (at 30% MVC), coefficient of variation (CoV) of force and of the discharges rates of motor units from the vastus medialis obliquus and vastus lateralis were determined as subjects performed 20% and 30% MVC knee extension contractions before and after training. CoV of motor unit discharges rates was significantly reduced for both muscles following strength training (P < 0.001), but did not change in the endurance (P = 0.875) or control group (P = 0.995). CoV of force was reduced after the strength training intervention only (P < 0.01). Strength training, but not endurance training, reduces motor unit discharge rate variability and enhances force steadiness of the knee extensors. These results provide new insights into the neuromuscular adaptations that occur with different training methods.     

Effective muscle elongation positions for the neck extensor muscles: An ultrasonic shear wave elastography study

This study aimed to clarify the effective stretching positions for neck extensor muscles. Fifteen healthy men were measured shear moduli of the right neck extensor muscles using ultrasound shear wave elastography in following positions: rest (Rest), flexion (Flex), contralateral bending (Bend), flexion + contralateral bending (Flex → Bend), flexion + contralateral bending + contralateral rotation (Flex → Bend → ConRot), and flexion + contralateral bending + ipsilateral rotation (Flex → Bend → IpsRot). The increase in the shear modulus indicated a greater muscle elongation. Regarding the upper trapezius and splenius capitis, the shear moduli at Flex → Bend, Flex → Bend → ConRot, and Flex → Bend → IpsRot were significantly higher than those at Rest. The shear moduli at stretching positions, including contralateral bending, were significantly higher than those at Rest and Flex in the levator scapulae. The results indicated that the stretching position with a combination of flexion and contralateral bending could be effective for elongation of the upper trapezius and splenius capitis. Furthermore, the stretching positions including contralateral bending could be effective for the levator scapulae.     

A compensation of angular displacements of the hip joints and lumbosacral spine between subjects with and without idiopathic low back pain during squatting

Low back pain (LBP) is one of the most common symptoms reported in adults. However, the contribution of postural control on the lumbar spine and hips during squatting has not been carefully investigated in individuals with LBP. The aim of this study was to compare three-dimensional kinematic changes of the lumbar spine and hips between subjects with and without idiopathic chronic LBP during squatting activities. In total, 30 subjects enrolled in the study (15 control subjects and 15 subjects with idiopathic chronic LBP). All participants were asked to perform squatting activities five times repeatedly while holding a load of 2 kg in a basket. The outcome measures included the Oswestry Disability Index (ODI) and kinematic angular displacement for the hips and lumbar spine. The LBP group demonstrated increased range of motion (ROM) in flexion of the dominant (T = ?2.14, p = 0.03) and non-dominant (T = ?2.11, p = 0.03) hips during squatting. The lumbar spine flexion ROM significantly decreased (T = 2.20, p = 0.03). The kinematic changes demonstrated interactions with region × group (F = 5.56, p = 0.02), plane × group (F = 4.36, p = 0.04), and region × plane (F = 2292.47, p = 0.001). The ODI level demonstrated significant interaction on combined effects of body region and plane (F = 4.91, p = 0.03). Therefore, the LBP group utilized a compensation strategy to increase hip flexion with a stiffened lumbar spine in the sagittal plane during squatting. This compensatory kinematic strategy could apply to clinical management used to enhance lumbar spine flexibility in subjects with idiopathic chronic LBP.     

Isometric back muscle endurance: An EMG study on the criterion validity of the Ito test

The validity of the Sorensen test as a measure for back muscle endurance is controversial due to a possible impact of hip extensor muscles. The aim of this study was to investigate the criterion validity of an alternative test (Ito test) compared to the Sorensen test. Both procedures were performed by 29 healthy subjects (11 women) for 5 s and until exhaustion (randomized order). EMG activity was measured from 3 lumbar back and 3 hip extensor muscles. Muscular involvement in test positions was calculated as percentage of maximal voluntary contraction (MVC). Muscle fatigue was determined by the normalized regression coefficient of the median frequencies of the EMG power spectrum (NMF_slope). Prediction of holding time by NMF_slope values was investigated using regression analysis. In the test positions, the hamstring muscles were activated to a higher MVC percentage in the Sorensen than in the Ito test, while the iliocostalis muscle was less activated. Similarly, the iliocostalis (p = 0.006) and the multifidi muscles (p = 0.03) significantly contributed to predict holding time in the Ito test, whereas the multifidi muscles (p = 0.001) and the semitendinosus muscle (p = 0.046) did so in the Sorensen test. The results of this study indicate that the Ito test might present a valuable alternative for testing back muscle endurance in LBP patients.     

Voluntary activation of the trapezius muscle in cases with neck/shoulder pain compared to healthy controls

Subjects reporting neck/shoulder pain have been shown to generate less force during maximal voluntary isometric contractions (MVC) of the shoulder muscles compared to healthy controls. This has been suggested to be caused by a pain-related decrease in voluntary activation (VA) rather than lack of muscle mass. The aim of the present study was to investigate VA of the trapezius muscle during MVCs in subjects with and without neck/shoulder pain by use of the twitch interpolation technique.Ten cases suffering from pain and ten age and gender matched, healthy controls were included in the study. Upper trapezius muscle thickness was measured using ultrasonography and pain intensity was measured on a 100 mm visual analog scale (VAS). VA was calculated from five maximal muscle activation attempts. Superimposed stimuli were delivered to the accessory nerve at peak force and during a 2% MVC following the maximal contraction.Presented as mean ± SD for cases and controls, respectively: VAS; 16.0 ± 14.4 mm and 2.1 ± 4.1 mm (P = 0.004), MVC; 545 ± 161 N and 664 ± 195 N (P = 0.016), upper trapezius muscle thickness; 10.9 ± 1.9 mm and 10.4 ± 1.5 mm (P = 0.20), VA; 93.6 ± 14.2% and 96.3 ± 6.0% (P = 0.29).In spite of significantly eight-fold higher pain intensity and ∼20% lower MVC for cases compared to controls, no difference was found in VA. Possible explanations for the reduction in MVC could be differences in co-activation of antagonists and synergists as well as muscle quality.     

Changes in EMG activity during clenching in chronic pain patients with unilateral temporomandibular disorders

The study assessed the differences in electromyographic (EMG) activity recorded during clenching in women with chronic unilateral temporomandibular disorders (TMDs) as compared to control subjects. Seventy-five full dentate, normo-occlusion, right-handed, similarly aged female subjects were recruited. Twenty five subjects presented with right side TMD, 25 presented with left side TMD and 25 pain-free control subjects participated. Using integrated surface EMG over a 1 s contraction, the anterior temporalis and masseter muscles were evaluated bilaterally while subjects performed maximum voluntary clenching. Lower EMG activation was observed in patients with TMD as compared to control subjects (temporalis: 195.74 ± 18.57 vs. 275.74 ± 22.11, P = 0.011; masseters: 151.09 ± 17.37 vs. 283.29 ± 31.87, P < 0.001). An asymmetry index (SAI) was calculated to determine ratios of right to left sided activation. Patients with right-sided TMD demonstrated preferential use of their left-sided muscles (SAI ?5.35 ± 4.02) whereas patients with left-sided TMD demonstrated preferential use of their right-sided muscles (SAI 6.95 ± 2.82), (P = 0.016). This unilateral reduction in temporalis and masseter activity could be considered as a specific protective functional adaptation of the neuromuscular system due to nociceptive input. The asymmetry index (SAI) may be a useful measure in discriminating patients with right vs. left-sided TMD.     

Validity of trunk extensor and flexor torque measurements using isokinetic dynamometry

This study aimed to evaluate the validity and test–retest reliability of trunk muscle strength testing performed with a latest-generation isokinetic dynamometer. Eccentric, isometric, and concentric peak torque of the trunk flexor and extensor muscles was measured in 15 healthy subjects. Muscle cross sectional area (CSA) and surface electromyographic (EMG) activity were respectively correlated to peak torque and submaximal isometric torque for erector spinae and rectus abdominis muscles. Reliability of peak torque measurements was determined during test and retest sessions. Significant correlations were consistently observed between muscle CSA and peak torque for all contraction types (r = 0.74−0.85; P < 0.001) and between EMG activity and submaximal isometric torque (r ⩾ 0.99; P < 0.05), for both extensor and flexor muscles. Intraclass correlation coefficients were comprised between 0.87 and 0.95, and standard errors of measurement were lower than 9% for all contraction modes. The mean difference in peak torque between test and retest ranged from −3.7% to 3.7% with no significant mean directional bias. Overall, our findings establish the validity of torque measurements using the tested trunk module. Also considering the excellent test–retest reliability of peak torque measurements, we conclude that this latest-generation isokinetic dynamometer could be used with confidence to evaluate trunk muscle function for clinical or athletic purposes.     

Associations between cervical and scapular posture and the spatial distribution of trapezius muscle activity

The first aim of this investigation was to quantify the distribution of trapezius muscle activity with different scapular postures while seated. The second aim of this investigation was to examine the association between changes in cervical and scapular posture when attempting to recruit different subdivisions of the trapezius muscle. Cervical posture, scapular posture, and trapezius muscle activity were recorded from 20 healthy participants during three directed shoulder postures. Planar angles formed by reflective markers placed on the acromion process, C7, and tragus were used to quantify cervical and scapular posture. Distribution of trapezius muscle activity was recorded using two high-density surface electromyography (HDsEMG) electrodes positioned over the upper, middle, and lower trapezius. Results validated the assumption that directed scapular postures preferentially activate different subdivisions of the trapezius muscle. In particular, scapular depression was associated with a more inferior location of trapezius muscle activity (r = 0.53). Scapular elevation was coupled with scapular abduction (r = 0.52). Scapular adduction was coupled with cervical extension (r = 0.35); all other changes in cervical posture were independent of changes in scapular posture. This investigation provides empirical support for reductions in static loading of the upper trapezius and improvements in neck posture through verbal cueing of scapular posture.